Butterflies are one of the most popular and easily recognized groups
of insects. Together with moths, they make up one of the major insect
orders or groups—Lepidoptera —which number some 160,000 recognized species
worldwide. There are over 250 species of butterflies in the Sonoran Desert.

Queen butterfly

Lepidoptera comes from Greek words meaning scaled and wing. Butterflies
and moths can easily be distinguished from other insects by their wings,
which are covered with thousands of tiny overlapping scales, much like
tiles on a roof. Each scale is one color, but collectively a butterfly’s
color pattern is produced by a complex mixture of differently colored
scales. Butterflies are usually large, pretty, and diurnal. They are rarely
pests, and consequently are well-liked by humans.

Dispersal and Species Richness

There are a number of factors to account for the rich butterfly diversity
in the Sonoran Desert. In general, as one approaches the tropics, species
richness increases. Also, a varied topography means a corresponding variety
of microclimates, rainfall patterns, plant distributions, and therefore
butterfly distributions.

The majority of butterfly species in the Sonoran Desert are rather sedentary,
occurring in fairly close proximity to their larval foodplants. But at
times, for reasons not fully understood, butterflies wander. Some species
move at a particular season, some nearly any time. Some species are true
migrants, in that individuals push northward early in the season and southward
later. However, an interesting array of taxa are influx species, entering
the Sonoran Desert yearly from other deserts, thornscrub habitats, and
mountain ranges in northwestern Mexico. The strength, time of onset, and
duration of the summer rainy season are thought to be responsible for
the intensity of this influx phenomenon. Many of these visitors breed
in the Sonoran Desert and comprise a significant or even dominant portion
of the summer butterfly fauna. Several influx species, however, are on
dead-end missions, there being no suitable plants to serve as larval hosts.
The fact that there are both indigenous and influx species of butterflies
in the Sonoran Desert accounts for the high number of species, and also
delights the butterfly enthusiast.

Life Cycle

The life cycle of butterflies is one of the true miracles in nature.
Butterfly lives have four distinct stages: egg, caterpillar (or larva),
chrysalis (or pupa), and adult. The term describing this series of distinct
stages of development is complete metamorphosis, as distinguished from
simple or incomplete metamorphosis, in that the animal progresses through
life stages which are very similar to each other. (See the “grasshoppers”
section for an example of incomplete metamorphosis.)

In most cases, butterflies produce one or more generations (broods) per
year. The length of the complete life cycle varies greatly, ranging from
weeks to a couple of years or more in desert adapted species. The lifespan
of an adult butterfly varies as well, from merely a few days to as long
as several months. After mating, butterflies oviposit (lay eggs), either
singly or in clusters. Female butterflies typically oviposit on specific
groups of related plants that will provide food for the caterpillars.
The young caterpillars begin feeding and, because their skins do not expand
to accommodate growth, must shed their skins several times. Each stage
between molts is called an instar; each instar is larger than the previous
one. The final molt produces a pupa, the resting stage during which the
animal does not feed but undergoes the amazing transformation into a butterfly.
The pupa of many butterflies hangs from a silk button called a cremaster.
Other species’ pupae are held upright by a silken girdle. Some are disguised
(cryptic), being generally green or brown and resembling leaves, stems,
or wood. Others are covered in thornlike tubercles or bumps. Just prior
to the emergence of the butterfly, the chrysalis usually changes color.
Once free of the chrysalis, the butterfly pumps fluid from its swollen
body to its shrunken wings. The newly emerged butterfly then lets its
wings dry and harden before taking flight in search of food and a mate.

The Importance of Butterflies

Butterflies are important pollinators. They are also good indicators
of the ecological quality of a habitat, as they are important components
of the food chain, particularly as larvae. Few butterflies are a serious
threat to economically important plants. In short, butterflies are benign,
aesthetically pleasing, faunal members. In turn, the main threat to butterflies
is the destruction and loss of their habitats. The channelization of riparian
areas, draining of wetlands, lowering of water tables, growth of cities,
and expansion of agriculture all contribute to this habitat loss. Widespread
use of pesticides may also threaten healthy butterfly populations.

The Butterfly Families

Swallowtails (Papilionidae):

Pipevine swallowtail

Swallowtails are mostly tropical and include some of the largest butterflies
in the world. Adults of both sexes have 6 walking legs, take nectar readily,
and often flutter their wings even while perched. One of our region’s
largest butterflies, with a 4 inch (10 cm) wingspread, is the giant swallowtail
(Papilio cresphontes, also called Heraclides cresphantes), a brown and
yellow species commonly encountered in urban areas. Its larvae, which
feed mostly on the leaves of citrus, look much like fresh bird droppings.
If the larvae are touched or disturbed, an unpleasant-smelling, y-shaped
orange organ called an osmeterium, is everted from just behind the head.
This device and the cryptic appearance are adaptations to avoid predators
and perhaps parasites.

Another impressive swallowtail is the pipevine swallowtail (Battus philenor),
which is slightly smaller than the giant swallowtail. Pipevine swallowtails
are commonly encountered March through October. The butterfly’s upper
surface is a dark, iridescent blue; the underside is blue with orange
spots. The showy, red-orange caterpillars are poisonous due to the compounds
taken from the leaves of pipevines (Aristolochia spp.), their larval food
plant. The bright colors serve as warnings to would-be predators that
the caterpillars are highly distasteful.

Whites and Sulphurs (Pieridae):

Butterflies in this family are small- to medium-sized and most often
white, yellow, or orange, with black margins. Some are among the first
spring butterflies, even as early as January. Many emerge in a series
of broods throughout the year. Still others are influx species during
and after the summer monsoons. This family often exhibits mud puddling
behavior wherein dozens of individuals group together on a patch of damp
mud to drink and take in minerals and salts. One of the more showy species,
the southern dogface (Colias cesonia, also called Zeren cesonia), has
a distinctive outline of a poodle on each forewing. A common species,
the cloudless sulphur (Phoebis sennae), exhibits strong sexual dimorphism
in which the males and females have visibly different wing patterns or
coloration. Males of this species are bright, clear, lemon yellow, while
females are off-white with small dark markings. In addition to sexual
dimorphism, some sulphur species, such as the tailed orange (Eurema proterpia),
are seasonally dimorphic, there being short and long day-length color
patterns evident. Early spring is a good time to search for orange-tips.
The Sara orange-tip (Anthocharis sara) and desert orange-tip (Anthocharis
cethura) both come to flowering wild mustards, plants that also serve
as larval food plants for these butterflies.

Gossamer Wing Butterflies (Lycaenidae):

Lycaenidae is a large family of small butterflies. Despite their size,
many are detailed with exquisite markings—truly jewels of the insect world.
One of the world’s smallest butterflies, the pygmy blue (Brephidium exile),
measures little more than ½ inch (12 mm) from wingtip to wingtip,
and is fairly common in our region, especially in disturbed areas. The
great blue hairstreak (Atlides halesus) is one of the largest and most
spectacular of the gossamer wings, but it is solitary and uncommon. The
caterpillars feed on desert mistletoes (Phoradendron spp.). While there
are several broods during the year, the best places and times to look
for great blue hairstreaks are wherever and whenever desert broom or seep-willow
(both Baccharis spp.) are in bloom.

Metalmarks (Riodinidae):

This largely tropical family is extremely diverse in appearance and in
species content. Fewer than a dozen species occur in the Sonoran Desert;
most of these having metallic spotting on the ventral (underside) surface
of the wings. Metalmarks have long antennae for their size and usually
perch with their wings opened flat. One species, the Mormon metalmark
(Apodemia mormo), is quite variable from one location to the next, but
all populations are associated with patches of various buckwheat (Eriogonum
species).

Snout Butterflies (Libytheidae):

Snout butterfly

The single species of snout butterfly that occurs in the Sonoran Desert,
the American snout butterfly (Libytheana bachmanii), can have huge population
surges, particularly in the summer and fall, though in some years it is
nearly absent. It has a wingspan of about 1¾ inch (44 mm) and is
easily recognized by the long projecting sense organs called palpi (which
resemble snouts) located between the antennae. The larvae feed on desert
and netleaf hackberry.

Brush-footed Butterflies (Nymphalidae):

This is a very large and diverse family with most species medium-sized
and generally orange and brown. Many well-known butterflies belong to
this family, such as fritillaries, painted ladies, crescents, checker-spots,
anglewings, admirals, longwings, and of course, monarchs. Nymphalid caterpillars
feed on a wide variety of plant families. Most larvae are fiercely spined,
and their pupae are usually sharply angled and adorned with silver or
gold colors.

The gulf fritillary (Agraulis vanillae) is a large, vividly-colored,
orange and black butterfly with brilliant silver spots on the underside.
Gulf fritillary caterpillars feed exclusively on passion vines. Planting
ornamental passion vines around the house can greatly increase the abundance
of these butterflies.

One subgroup of the brushfoots, the milkweed butterflies (Danainae),
is probably among the most noted and studied groups of butterflies, since
it contains the monarch (Danaus plexippus). This well known species is
a remarkably strong flier, migrating great distances every year to overwintering
roosts in California and central Mexico. The monarch butterfly is not
very common in the Sonoran Desert, but it can be seen regularly in late
summer and early fall on its push southward. A much more common resident
of the region, the queen (Danaus gilippus), is closely related to the
monarch. The larvae of both species feed exclusively on various plants
in the milkweed family (Asclepiadaceae). This family of plants is poisonous
to most vertebrates, and the milkweed butterflies gain protection by ingesting
its leaves.

Skippers (Hesperiidae):

This family is named for its rapid, skipping flight. Skippers are small-
to medium-sized, differing from other butterflies in having larger bodies
in proportion to the wings. They generally have broader heads and hooked
antennae that continue past the clubs rather than ending at them. To some
people, skippers resemble moths, being hairier and more robust and generally
lacking the gaudy colors and patterns of the other butterfly families.
But unlike most moths, most skippers are day-flying or crepuscular. Many
skipper larvae feed on grasses. One common garden species, the fiery skipper
(Hylephila phyleus), eats Bermuda grass and is common around desert lawns.
Another common species, the funereal duskywing (Erynnis funeralis), is
mostly dark, with white fringes on the hind wings’ edges. It is regular
both in towns and in desert arroyos, often in close proximity to woody
legumes, the larval hosts. Several skipper species have long tail-like
projections on the hindwings. The most common of these, the dorantes long-tail
(Urbanus dorantes), is an influx species and is at times abundant in late
summer and fall.

Butterfly or Moth?

Though butterflies and moths appear similar in many respects, there are
some ways to distinguish between them. Generally when a butterfly lands
and rests on a plant it holds its wings vertically, while moths tend to
rest with their wings folded back almost horizontally. Moths have heavy,
furred bodies, whereas the butterflies have more delicate, slender bodies
with little hair. Butterfly antennae are thin and end with a knob at the
tip. Moth antennae are often feathery and without a knob.

Color is not a reliable indicator, as some of the moths, especially the
Saturnids, are beautifully colored and some butterflies, such as satyrs
and mourning cloaks, have muted coloration. Also, not all moths are night
fliers. Some species, such as the buck moths and the Calleta silk moth,
fly by day. (You may notice the Calleta moth as it feeds on ocotillo leaves
during the summer rainy season. Look for ocotillos stripped of leaves
from the top down.)

Both butterflies and moths lay eggs which hatch into caterpillars. These
caterpillars molt into a pupa, or resting stage. After a period of time—a
few days to a season—the winged adult emerges from the pupal case. Moths
tend to construct cocoons, protective silk coverings around themselves,
before molting into pupas. Butterflies do not encase themselves in cocoons.